FAA Powerplant Written Practice Test

What is the primary function of cascade vanes in a thrust reversing system?

1. To increase overall engine efficiency

2. To turn the fan airstream in a forward direction

3. To enhance the lift of the aircraft

4. To regulate the fuel flow

The correct answer is: To turn the fan airstream in a forward direction

The primary function of cascade vanes in a thrust reversing system is to redirect the bypass airflow produced by the engine. When the vanes are deployed, they effectively turn the fan airstream in a forward direction, which helps to create a reverse thrust. This action aids in decelerating the aircraft upon landing, allowing for shorter stopping distances and improving safety during landings, especially in adverse conditions. Cascade vanes are designed to create a controlled alteration in the airflow direction, allowing the engine's thrust to act in the opposite direction of the aircraft's movement. This capability is crucial for thrust reversers, as they enhance the braking performance of an aircraft without solely relying on wheel brakes, which can generate heat and wear out more quickly. The other options do not accurately describe the role of cascade vanes. For instance, while increasing engine efficiency is a goal of many design features, it is not a direct function of cascade vanes in thrust reverse systems. Similarly, enhancing the lift of the aircraft or regulating fuel flow does not relate to the purpose of cascade vanes, which is specifically focused on altering airflow to achieve reverse thrust.